Question

Next, let's refresh on graphing basics. Here we'll ask you to look at the graphed data for the Haber Process again, this time identifying the parts of the graph that show us how we set up the experimental process. Be SURE to review your Guided Notes if you need a refresher!

Answer 1

Good — here’s a simple checklist and how-to for reading a Haber Process graph so you can pick out which parts show how the experiment was set up and altered.

Quick reminders about the chemistry
- Reaction: N2 + 3 H2 ⇌ 2 NH3 (exothermic).
- Le Chatelier: increasing pressure or removing NH3 shifts equilibrium toward products; increasing temperature favors reactants. A catalyst speeds approach to equilibrium but does not change the equilibrium composition.

Step‑by‑step: how to identify experimental setup on the graph
1. Check the axes, legend and units
- x‑axis: usually time (how the experiment was run).
- y‑axis: concentration, partial pressure, or % composition of N2, H2, NH3, or total pressure.
- Make sure you know what each curve/color/marker represents.

2. Find t = 0 and the initial conditions
- The starting concentrations/pressures at t = 0 tell you the initial mixture and whether the reaction was started from only reactants or from a mixture.
- A nonzero initial NH3 means product was present at the start.

3. Identify the reaction start and basic behavior
- A smooth increase of NH3 and simultaneous decrease of N2 and H2 after t = 0 = reaction started then.
- The rate of change (slope) at early times is the initial reaction rate.

4. Locate equilibrium (plateau)
- When curves flatten and values stop changing, the system has reached equilibrium. Those plateau values are the equilibrium concentrations/pressures.
- Time to reach plateau = time to equilibrium under those conditions.

5. Spot deliberate experimental changes
- Sudden jumps or kinks in a curve indicate a change in conditions: adding or removing gas, changing pressure, changing temperature, or turning on/off a catalyst.
- Example signatures:
- Sudden increase in total pressure or a shift to more NH3: pressure was increased.
- Sudden drop in NH3 with increase in N2/H2: product removed.
- After a jump, the system moves to a new plateau (new equilibrium) — that shows how the stress changed equilibrium.
- If at some time the slope becomes steeper but final plateau stays same: a catalyst was likely added (faster approach, same equilibrium).
- If final NH3 concentration decreases after increasing temperature: temperature was raised (exothermic reaction shifted left).

6. Use slopes quantitatively
- Steeper slope = faster rate. You can draw tangent lines early in the curves to compare rates before and after a change.
- Compare initial slopes of catalyzed vs uncatalyzed runs.

7. Look for experimental detail cues
- Error bars and replicate curves indicate measurement precision and reproducibility.
- Annotations, arrows, or vertical dashed lines often mark times when an experimental manipulation was made (e.g., “pressure increased at t = 120 s”).

Common scenarios and what to read from the graph
- NH3 rises to plateau while N2 and H2 fall: normal approach to equilibrium from reactants.
- At time t1 NH3 suddenly drops and N2/H2 rise, then a new plateau: product removed at t1 (shift according to Le Chatelier).
- At time t2 slopes get steeper but plateaus unchanged: a catalyst was added at t2.
- After a temperature increase, NH3 plateau lowers: temperature was increased (favors reactants for exothermic forward reaction).
- After a pressure increase, NH3 plateau rises: pressure was increased (favors side with fewer moles of gas).

What to do next
- If you have the specific graph, upload it or paste the image/data and I’ll point out exactly where the experimental set‑ups and changes are and explain what each change means for the Haber equilibrium.